The invention relates to an electrical circuit breaker having a sealed casing made of moulded insulating material, filled with an insulating gas with high dielectric strength, notably sulphur hexafluoride, and comprising:
a system of separable contacts actuated by means of an operating mechanism,
a pair of connection terminals in electrical connection with said contacts via bushings of conducting material, passing through the wall of the lateral surface of the casing and extending perpendicular to the longitudinal axis,
and means of fixing the insulating casing to a metal support electrically connected to the ground or earth.
A puffer circuit breaker of the kind mentioned is described in French Pat. No. 2,441,916 filed by the applicant. The circuit breaker comprises a main circuit having a fixed main contact operating in conjunction with a movable main contact, and an auxiliary shunting circuit having a fixed arcing contact and a movable arcing contact. Inside the oblong casing, the main circuit is connected directly to the connection terminals extending along a trajectory directly adjacent and shorter than that of the auxiliary circuit. Opposite from the connection terminals, the circuit breaker is equipped with fixing studs cast with the insulating casing, and comprising inserts to receive screws when the circuit breaker is secured to the metal support at ground potential. The external lateral surface of the casing is smooth, which gives rise to a problem of electrical insulation and dielectric withstand of the circuit breaker in the presence of a high rated voltage, for example greater than 20 kV. It is then imperative that the dimensions of the casing be increased to adapt the distance in the air to the minimum value laid down by standards. Modifying the casing gives rise to an increase in dimensions and in the cost of manufacturing the circuit breaker.
The object of the invention consists in increasing the electrical insulation of a puffer circuit breaker without increasing the internal dimensions of the casing filled with insulating gas of high dielectric strength.